duplicate conc values can occur via cmaxes, which causes error in pre…

[mduncans]

…dict_with_exposure_plot. adding failing test showing conc column is not unique.

[mduncans]

opening PR to run tests to confirm failing on CI.

[mduncans]

Initial failing mode calling predict_with_exposure_plot where cmaxes contained value already in compute_exposure_predictions:

> predict_with_exposure_plot(
+       data_proc,
+       mod,
+       CONC,
+       treatment_predictors = list(
+         CONC = 10,
+         deltaQTCFBL = 0,
+         TRTG = "Dofetilide",
+         TAFD = "1 HR"
+       ),
+       control_predictors = list(
+         CONC = 0,
+         deltaQTCFBL = 0,
+         TRTG = "Placebo",
+         TAFD = "1 HR"
+       ),
+       cmaxes = c(100)
+     )
Error in `$<-.data.frame`:
! replacement has 2 rows, data has 1
Show Traceback

Now with unique call, correctly runs

> predict_with_exposure_plot(
+     data_proc,
+     mod,
+     CONC,
+     treatment_predictors = list(
+         CONC = 10,
+         deltaQTCFBL = 0,
+         TRTG = "Dofetilide",
+         TAFD = "1 HR"
+     ),
+     control_predictors = list(
+         CONC = 0,
+         deltaQTCFBL = 0,
+         TRTG = "Placebo",
+         TAFD = "1 HR"
+     ),
+     cmaxes = c(100)
+ )
>